1. Field of the Invention
The present invention relates to a semiconductor device having a controller capable of transmitting and receiving information to and from an external apparatus, and in particular, to a semiconductor device capable of responding to a command received from an external apparatus within a specified period after the device has been powered on, and a memory card having the semiconductor device.
2. Description of the Related Art
In recent years, various memory cards have been emerging. If a certain type of memory card receives a predetermined command immediately after being supplied with power, it must immediately notify a host apparatus of information indicating the capacity of a memory and the like. The notification of this information must be carried out within a period defined in the specifications of the memory card.
Commands sent by the host apparatus are processed through, for example, a CPU mounted in a controller that controls the memory. Immediately after a power supply, a setup process is executed which relates to the oscillation of a clock required to operate the CPU as well as the setting of a phase locked loop (PLL). The CPU can start normal operations after the setup process has been completed. Thus, a long time may be required by the memory card to enter a standby state (the state in which the memory can respond to an access command from the host apparatus). As a result, the memory card may fail to notify the host apparatus of information indicating the capacity of a memory and the like within the period defined in the specifications of the memory card.
Jpn. Pat. Appln. KOKAI Publication No. 9-062808 discloses a technique for improving an operation performed until a supplied voltage reaches a predetermined operation voltage; the operation tends to be unstable.
This document states that while the supplied voltage remains at a specified value or less, an internal circuit is reset and thus ensured to perform normal operations. However, according to this document, the memory card cannot process a command sent by the host apparatus and notify the host apparatus of the information indicating the capacity of the memory or the like which the command requires, before entering the standby state after power-on.
It is thus desired to present such a technique as enables the memory card to notify the external apparatus of the predetermined information before entering the standby state.